Codepipeline Triggered Webhook Event and Codebuild-Buildspec Environment Variables

When using AWS CodePipeline triggered by a GitHub webhook event (such as a pull request or push), accessing the specific event type that triggered the pipeline within your buildspec.yml can be challenging, especially when using CodeStar Connections as the source.

The CODEBUILD_WEBHOOK_TRIGGER environment variable, which typically provides information about the webhook event that triggered the build, is not available when CodeBuild is triggered through CodePipeline. This is because CodeBuild is not directly triggered by the webhook in this case, but rather by CodePipeline.

Unfortunately, CodePipeline does not automatically pass the webhook event type to CodeBuild as an environment variable. The SourceVariables you mentioned from the CodeStar connection do not provide information about the event type that triggered the pipeline.

To work around this limitation, you have a few options:

1. Custom Environment Variables: You can set up custom environment variables in your CodePipeline stage that passes information to CodeBuild. However, this would require additional setup and possibly a Lambda function to determine the event type and set the variable.

2. Source Code Examination: In your buildspec.yml, you could potentially examine the source code or commit information to infer what type of event occurred. For example, you could check for the existence of a pull request number or examine branch names.

3. GitHub Actions: If possible, you could use GitHub Actions in combination with your AWS setup. GitHub Actions can easily distinguish between different event types and could trigger your pipeline with custom payloads containing the event information.

4. AWS EventBridge: You could set up an EventBridge rule to capture GitHub webhook events and trigger your pipeline, passing along the event type as a parameter.

While these workarounds can help, it's important to note that there isn't a straightforward, built-in way to access the original GitHub webhook event type in CodeBuild when it's triggered through CodePipeline using a CodeStar connection. This is a limitation of the current integration between these services.
Sources
Environment variables in build environments - AWS CodeBuild
AWS Code Pipeline v2 pipeline level variable not resolving in code build | AWS re:Post